Path matching in TypeScript to allow type-safe extraction of path params as union type

pathMatcher.ts

// ID for the parameter
type ParamId<T> = T;

type ParamKey<Component> = Component extends `:${infer NameWithPattern}`
  ? `param_${ParamId<NameWithPattern>}`
  : never;

type ParamKeys<Path> = Path extends `${infer Component}/${infer Rest}`
  ? ParamKey<Component> | ParamKeys<Rest>
  : ParamKey<Path>;

type Keys = ParamKeys<"/:a/user/:b/:c">;


// This is a really cool trick:
//    1. Recursive tyepes
//    2. Template literal types to extract the components from the provided path.
//    3. Note that this only works at compile time using compile-time constants. Otherwise the whole thing falls apart.
// If you don't have compile-time constants, things could still fail at runtime.
const x: Keys = "param_a";